This invention relates to oscillator circuits and, more particularly, to crystal-controlled oscillator circuits amenable to integrated circuit manufacturing techniques.
A wide variety of oscillator circuits are known in the art, including crystal-controlled oscillator circuits, some of which are suitable in varying degrees for integrated circuit manufacture. A major difficulty has been to achieve a high level of integration without sacrificing such desirable characteristics as circuit simplicity, frequency range, frequency precision, and frequency and duty cycle stability. In the oscillator circuit disclosed in my U.S. Pat. No. 3,979,693 of Aug. 13, 1976, for example, clipping and duty cycle control circuitry are connected to the oscillator to provide a square-wave output signal having a 50 percent duty cycle. AGC circuitry is provided therein for controlling the oscillator gain to achieve amplitude and frequency stability. Both the duty cycle control and the AGC circuitry require filtering capacitors. Ideally, such an integrated circuit oscillator would include no capacitive or inductive elements (except for the resonant means), no special circuitry for duty cycle or frequency stability control, and no discrete external elements except perhaps for the resonant means, such as a piezoelectric crystal in the case of crystal-controlled oscillators.